The question that has plagued every Yahoo CEO for the last 10 years or so is a pretty simple one: What does Yahoo do?

Marissa Mayer, six months on the job now, seems to have come up with a pretty good answer.

She debuted it this morning in a keynote interview at the World Economic Forum in Davos.

She said that the Web has become "vast" with content, and that what Yahoo can do is use all the contextual clues it has about its users – their "social context," their specific location, their activity on Yahoo and elsewhere – "to make sense of the content."

In short, what Marissa Mayer's Yahoo will do is present "The Internet, ordered for you."

"We provide a feed of information that is ordered – a web, ordered for you, [that] is also available on your mobile phone."

"Which is interesting," she said, "because it brings Yahoo back to its roots."

That's the kind of vision that will excite Yahoo shareholders, employees, users and clients.

Unfortunately, Mayer says it's not going to happen right away.

Personalization that fully takes advantage of "personalized notions" – "things like likes on Facebook, tweets, articles you click on" – "will probably happen in the next three to five years," Mayer told the audience.